Polymer resins, including PET, are commonly employed in the plastic packaging industry. Because of its favorable processing properties, and because PET is considered recycling-friendly, PET is widely used to produce numerous types of bottles and containers (which may herein be collectively referred to as simply “containers”). In the bottle industry, for example, bottle-grade PET usually has a resin intrinsic viscosity (IV) of about 0.65 to 0.87 dL/g, and is commonly used in connection with ISBM processing.
Extrudable PET compositions or formulations (e.g., extrudable PET co-polymers) are also known in the packaging industry. EBM PET can be desirable in connection with a number of applications, as it can permit the use of PET to form articles that are commonly formed from HDPE, for example, large plastic containers with handles. For PET to be suitable for EBM processes, a higher molecular weight PET, i.e., one having a higher IV (e.g., about 1.0 dL/g or greater) may be needed. However, such co-polymers are commonly amorphous, or slow-crystallizing, which can present certain conversion and reclamation challenges. While a slow-crystallizing co-polymer may allow for easier processing in EBM environments, the resulting container can, among other things, present recyclability challenges. For instance, when the material has not yet crystallized, and remains amorphous, it may melt at lower temperatures. Further, when amorphous or slow crystallizing resins are added to the PET recycling stream, the resins can cause, inter alia, unwanted sticking, thermal agglomeration, and bridging (or port plugging) issues. Such issues can make PET polymer resins unsuitable for conventional recycling programs and processes. Containers using Eastman EBO62 material fall into this category as can they present such recycling and performance issues since the PET resin is modified with additives for increased melt strength.
Moreover, if a bottle grade PET and an extrudable PET composition are blended or combined, so as to be provided in the form of branched PET copolymers, the resulting combination of resins may not exhibit performance characteristics that are sufficiently desirable. That is generally from a recycling standpoint, the higher percentage of extrusion-grade PET, the more undesirable the characteristics of the resulting product.
The use of standard ISBM-grade PET in the extrusion context might help to address some the aforementioned recyclability issues. However, for reasons such as noted above, such resins have generally not been successfully commercialized because of a number of challenges. Such resins typically have a low IV, i.e., commonly from about 0.65 to 0.87. As a result, they tend not to be able to carry their own weight and/or the resins may extrude too quickly to form a desired capturable parison. This presents a problem for most, if not all, EBM processes, which requires adequate melt strength in order to produce an acceptable parison (whether it be in a shuttle EBM system, a wheel EBM system, or any other). Without adequate melt strength, the parison will not form correctly and may flow too quickly (“like water”) to be captured by a blow mold. Additionally, with some articles, a lower IV may provide less container strength, more susceptibility to stress fractures or cracks, and undesirable visual haze or streaks.
Consequently, there remains a desire for an EBM method and system to produce commercially acceptable and bottles and/or containers that are compatible with the recycling stream from extrusion-grade PET compositions or formulations.